Micromechanical sensors for measuring acceleration, rotation rate, magnetic field and pressure, for example, are known and are manufactured for various applications in the automotive and consumer fields in mass production.
DE 10 2009 000 167 A1 describes an inertial sensor including two micromechanical planes. This allows sensor topologies to be implemented which enable considerable performance increases, for example with respect to an offset stability of acceleration sensors. A z-acceleration sensor is implemented, in which the movable mass is formed of two micromechanical layers (first and second MEMS functional layers) and in which capacitive evaluation electrodes are situated both beneath and above the movable structure, namely in the redistribution layer on the substrate wafer and in the second MEMS functional layer.
This so-called fully differential electrode system may be used to increase a capacitance distribution (capacitance/area) on the one hand, and also to achieve a good robustness with respect to substrate deformations (caused by assembly stress, for example) on the other hand. The former aspect results in an improved signal-to-noise ratio, the second in an improved offset stability of the sensor, among other things.
Furthermore, approaches are known in which a MEMS wafer and an evaluation ASIC wafer are mechanically and electrically connected to one another using wafer bonding methods, which is referred to as “vertical integration” or “hybrid integration” or “3D integration” and is known from U.S. Pat. No. 7,250,353 B2 or U.S. Pat. No. 7,442,570 B2, for example. In this way, it is possible to implement sensor topologies for inertial sensors with movements perpendicular to the chip level. A movable MEMS structure is situated on an evaluation ASIC, preferably a CMOS wafer, the uppermost metal layer of the ASIC acting as a fixed counter electrode.
An extension of the above-mentioned technology provides that, in addition to evaluation electrodes in the CMOS wafer, evaluation electrodes are provided in the MEMS wafer, as is known from DE 10 2012 208 032 A1, for example. In this way, an integration density, in the present case a capacitance per area of the components, may be increased, which may result in reduced noise and/or a smaller space requirement for the components.
From DE 10 2012 208 032 A1, a system including two micromechanical layers is known, which are linked with the aid of a vertical integration process. The MEMS wafer is manufactured in a surface micromechanical manner and is mechanically and electrically connected to an ASIC with the aid of a wafer bonding method. In addition to the substrate, the MEMS wafer has three polycrystalline silicon layers (one redistribution layer and two micromechanical layers), which may be structured largely independently of one another. Ultimately, the MEMS wafer thus includes two micromechanical functional layers and one strip conductor plane. The two micromechanical functional layers are joined to one another and form a single-piece or integral mass element. With the aid of through-silicon vias (TSV), which are formed in the ASIC wafer, an electrical connection to redistribution layers of the ASIC wafer may be implemented from the outside.
DE 10 2009 029 202 A1 describes a stacked arrangement of micromechanical components made up of multiple MEMS layers, in which a first MEMS structure is situated in one functional layer and at least one further MEMS structure is at least partially situated in at least one further functional layer. Such structures, in which the integration layer is also increased, may be implemented with the aid of a process which is known from DE 10 2009 000 167 A1.
Furthermore, vertically integrated components are known, in which two wafer stacks are bonded to one another, the two wafer bonds being formed by a MEMS wafer and a CMOS wafer, as is known from DE 10 2012 206 875 A1, for example, the MEMS wafer initially being applied to the CMOS wafer with the aid of a wafer bonding method, and thus in total a quadruple wafer stack is formed. This arrangement also allows an integration density of the components to be increased. The arrangement may be advantageous if the space requirement for MEMS functional structures and the electronic evaluation circuit are approximately equally large.
A wafer bond for a micromechanical inertial sensor is known from US 2013/0001710 A1, a blind hole being introduced into a first and a second MEMS functional layer, situated beneath the first, for the purpose of forming a sensor membrane for a capacitive pressure sensor. In this way, it is possible to suitably dimension a thickness of the sensor membrane.